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How flies evade the swat

Nicky Phillips

If you’ve ever attempted to swat a fly, you may have puzzled over how easily their agile little bodies evade death. Well wonder no longer.

Using super-fast cameras, US researchers have captured the wing and body movements of flies as they encounter a threat, namely a swat.

The videos show that with just a few beats of their wings, the pesky insects can execute a series of rapid banked turns that allow them to escape even the fastest human hand.

Just like a plane, a fly controls its orientation by rotating about three axes or dimensions; known as the yaw, pitch and roll.

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But the latest findings, published in the peer-reviewed journal Science, show the complex engineering of the most sophisticated planes have nothing on the elegant reflexes of the common fruit fly.

"These flies normally flap their wings 200 times a second and, in almost a single wing beat, the animal can reorient its body to generate a force away from the threatening stimulus and then continues to accelerate," University of Washington researcher and study leader, Florian Muijres, said.

Using three high-speed cameras operating at 7500 frames a second, the researchers watched as flies directed themselves away from a threat by quickly banking their bodies.

"Although they have been described as swimming through the air, tiny flies actually roll their bodies, just like aircraft in a banked turn, to manoeuvre away from impending threats," the supervising researcher from the University of Washington, Michael Dickinson, said.

The sequence of movements, including a counter-rotation to orient its body back on a horizontal plane, required nothing more than a few subtle changes in wing motion, Dr Dickinson said.

The getaway happened about five times faster than the flies’ normal in-flight turns, he said.

"We discovered that fruit flies alter course in less than one one-hundredth of a second, 50 times faster than we blink our eyes, and which is faster than we ever imagined,’’ Dr Dickinson said.

Previous research suggested flies escaped by yawing their bodies on the horizontal plane, a move that is roughly equivalent to how aeroplanes make small course corrections in cruising flight using their tail rudder.